Pershing 1A Maxi-Brute Clone 3D Printed
 

In the 70s I remember being at Service Merchandise and they had all the Maxi-Brutes, but I had only enough money to buy one. At the time it felt like the hardest decision of my life. I finally settled on the Honest John, but I always wanted the Pershing 1A too. I do have a TLP Pershing on the workbench, but it's just not the same. Then back at the end of March I decided to get a small 3D printer to give it a try, rocketry parts was one of the reasons. After a few weeks, I realized how useful 3D printing was and decided to buy a bigger better 3D printer, which opened up all kinds of possibilities. Then early last week I stumbled onto this thread by Leo Nutz on TRF https://www.rocketryforum.com/threa...a-clone.150742/.

Holy smokes!

Leo has done a really good job putting together the 3D files and making them available for the rest of us to use.

This is my first large 3D project I've attempted, plus I decided to use PETG since it can be way tougher and tolerate heat (aka Sun) than PLA. But PETG can be a challenge, especially with stringing. I had several fails at first printing the nose cone, but finally it came together. Leo recommended spiral/vase mode, which is single wall, but I couldn't get 0.8mm wall thickness Leo's parts are designed for, it was always too thin. Switching from a 0.4mm to 0.8mm nozzle would likely solve it, but I don't have one. So I printed mine double wall in Standard mode, combined with slower printing speed for PETG, my print time was a little over 30 hours combined for the 3 nose cone sections! So yeah, like Leo I can't offer to print these for anyone either, sorry. The results turned out great!

Here are the 3 sections that comprise the nose cone.

Here are the section dry fitted. My caliper measures my wall thickness as 0.80mm, and the combined weight of the nose cone parts dry fitted is 113 grams in total. Wow, it's huge!

Last night I printed one of the lower fins. Took about 2 and a half hours. Leo provided 2 versions of the upper and lower fins, one version is larger for flight like the Estes fins, and the other is scale. I'm printing the larger for the lower fins, although I might print the smaller scale fins for the the upper to help stability. The weight of the fin is 10 grams. 5 more to go!

At what point does it become less expensive to buy your own printer and plastic stock than to buy from Shapeways, Boyce, etc.

I'm seriously considering a printer, but only if the quality of home printed stuff is good enough and cheap enough to justify the effort.

That is a hard question with personal preferences mixed in. I'd liken it to changing your own oil versus taking it to a shop. I think it really comes down to how much of your time you are willing to put into it, how many uses you might have for 3D printing, and the personal satisfaction you can get from the I made that feeling. If you don't have a lot of time and much use for one, going the Shapeways/Boyce route is likely for the best. It can be a real time suck, especially if you also design your own parts. For this project I'm using the Amazon Basics PETG, which was $17.99 for a 1kg spool. So the nose was about $2.03 of material and the one fin about 18 cents. Your printer choice sort of depends on the quality you want coupled with how much time you are willing to invest in tuning the printer, versus having an out of the box experience. If you are willing to put the time into tuning the printer and printing parts to enhance it, you can get great results from the lower end printers versus a multi thousand dollar unit. My printer is a Creality CR-10S Pro, it was $650, but you can get decent printers like the Ender 3 that requires some assembly for a couple hundred. You just can't expect an out of the box experience like you can get with something like a MAKERBOT. I can't stress enough that if you buy one take the time at the beginning to learn how to level the print bed and how to make sure your prints stay adhered to the print bed during the printing process, it will save you a lot of frustration. The CR10S has been a much better experience than my MonoPrice in this respect. And there is the learning curve of how to setup your print settings and work with different kinds of plastics, but that you are going to encounter despite the printer. I did have a lot of frustrating failures are first trying to print this project, but now I think I have it down. I think my print at home results for quality is really good and the PETG is really tough stuff if printed properly. But then there is all that time waiting for the part to finish printing.......argh! On the flip side, my teenage daughter and I have had fun printing some non-rocketry projects too. I've also discovered several people here at work that have recently bought 3D printers, so we're sharing tips and experiences.

It seems that unless 3D printing becomes a hobby within the hobby, one would probably be better off purchasing finished parts, at least until prices, quality, and ease of use start falling into line. Thanks for your perspective. Looking forward to the finished model!

Tim (morley)-

Thanks for sharing your experiences here with the rest of us. I have wondered where Leo had run off to in recent years...sounds like he is spending his time on that OTHER forum....

Anyway, yes, your first-hand expereinces are just the kind of reports I have been wanting to read before jumping in myself. As tbzep said, I've been waiting for ease of use and, frankly, quality of output, to improve before jumping in. Even some of the stuff offered for commercial purposes, while improving, is still just a bit on the rough side for my personal tastes; but that is just me. But...it is getting better for sure. The photo of your Pershing fin looked great.

I really need to just purchase a commercial kit or part or two and do some full finish work on them to see just how much sanding, filling, and priming are necessary to get a good, quality finish on these parts.

Share more as you go, if you so desire. I suspect there are many here who want to learn and see more.

Thanks again.

Earl

Here is a closeup of the fin surface. I haven't sanded anything yet, the pictures are as they came off the printer. I printed at a 0.1mm resolution and the surface is very smooth, you can barely feel any of the layering.

I'm wondering where I'll wind up in total weight for the final rocket. The Estes catalog lists the Pershing 1A at 11.5 ounces (326.03 grams). Anybody have any real world weights for a finished Pershing? My BT-101 tube for this project weighs 88 grams. I'm going to set this up to accept the Estes E12-4, so I know that will require more nose weight than a D12-3 would. I believe there is roughly a 17.1 gram difference between a D12-3 and the E12-4 according to NAR data sheets.

If I don't forget, I'll weigh mine tonight. It's significantly underpowered with a D12-3. It's flight fishtailed and was considerably lower than my Centuri Saturn V, iirc. It was bad enough that I flew it one time and retired it immediately after. Back in those days I didn't fill spirals or prime under dark opaque paints like olive drab or artillery green. There was no heavy finishing work. The nose was just that heavy.

You will have better flights on a full 40 n-sec E15/18 or E28/30 Aerotech Composite.
All the 24 and 29mm BP SU engines from Estes are what I would call "barely adequate" for anything classified as a "Maxi Brute"; case in point, the 1/45 Little Joe II has ONLY the E30 as a suggested motor; ZERO BP motors.

I considered something more powerful, but you know, one of the most memorable rockets I had as a kid was my Maxi-Brute Honest John. Yeah, it barely lumbered off the pad under a D12-3, and there was that sometimes sick feeling in the pit of your stomach while you waited for the chutes to barely open just in time (they always did), but I loved it. It was always a crowd pleaser, I think because you could easily watch the whole flight close up. It was a real polar opposite to my desire to put the biggest engine I could fit into the smallest rocket approach.

I appreciate it. I figured a D12-3 would be stretched to it's limits, which is why I'm thinking an E12-4 would be a better choice. I'm not looking to send this into orbit, but I do want to make sure I can have a safe reliable flight. Your data point will help.

My Maxi-Honest John flew great on Estes D12-3 motors. If one thinks it is marginal on a D12, they haven't seen the Pershing on that motor!

Yeah, I don't think I'd classify the Honest John was marginal to the point of being unsafe or having poor flight characteristics, didn't mean to give that impression. But in comparison it was low and slow compared to most rockets. It always worked and flew up straight as an arrow. But it always did worry me waiting for the chutes to open. :-) Maybe more because it was the pride of my fleet and I didn't want to see it crash versus it being in real jeopardy. I have a Maxi-Brute Honest John in the works on my bench too, but it's an Estes kit, not a clone.

The Pershing sounds about like the Maxi X-Wing on a D12-3. It was a 'lob' at best. No time, really, for chutes to fully deploy before hitting the ground.

Next flight (and that was the last, 30 years ago) was on an Aerotech E. That was workable.


Earl

Mine is 11.8 oz including the OEM recovery system...and a lot of dust from hanging from the ceiling.

Thank you!

I have all three lower fins printed and one upper fin. I did print the smaller scale version of the fin Leo provided. For better or worse, I decided to go with the larger, it visually looks more proportional with the larger lower fins. The larger version weighs 13 grams and the smaller 11 grams.

I mentioned at the start of this thread I'm also building a TLP Pershing 1A. I started this before I got into 3D printing. I'm not building it stock, I'm making changes to make it look a little more like the Estes kit, I even decided to have the nose ejection break at the bottom like the Estes kit versus the small balsa nose at the tip. Trying to get the paper cones assembled for the nose was a bit of a pain to get to look right, it's not perfect, but it works. I wanted fins that had the dimensional profile of the real Pershing 1A, so I used aileron stock to achieve the lower and upper fin profiles, saves a lot of sanding. And I made the fin pads from balsa, that did take a lot of sanding, especially to get the tube contour right. I'm not quite done with the nose and I know I added some weight with the coupler to achieve the change to the nose ejection break point and there will be a little more to go to finished the cone. It doesn't have any nose weight added and it comes in at 111 grams, compared to 113 grams for the 3D printed cone. I have the inner core tube installed in the airframe, but not the engine mount yet. In total I'm at 235 grams so far for the TLP. Here are some pictures and a comparison of the nose cones between the TLP and the 3D printed.

Looking good

Thanks. I have one more upper fin to 3D print. But not much time to really work on it this weekend, my daughter is in a soccer tournament.

If I was building it, I would not even consider using a ridiculously small 24mm engine mount.
It should have a 29mm mount.
One can always adapt down but not up.

The TLP is already slated for a 29mm mount.

Fins printed. Printing cable covers and charge retainer next.

I've printed the last pieces from Leo's files. The cable covers, the charge retainers, and the shock cord plate. The combined weight of these last parts is about 26 grams.

long cable cover 9 grams
short cable cover 6 grams
charge retainer 2 grams each
shock cord plate 7 grams

I put all the printed parts on the scale at once to see what the combined weight was, figuring it to be a little more accurate since my scale is only accurate to 1 gram. 206 grams.

To help with adhesion of the fins to the body tube with epoxy, I am drilling small holes in the back. To ensure I don't accidentally drill through the front of the fin I am using my drill press so I can control the depth

Put the motor mount together. 24mm, I figure if I conclude the E12 won't lift it, there are 24mm composite options, like the E30. And if I crash it, I might be unhappy, but I can always build another. Since it might fly with an E30, I used a heavy wall BT-50 and added a third centering ring for a little extra strength, which is glued inside the body tube, used a long skewer to get the epoxy in the right place as I installed the mount. Also used the Estes Pro Series 24mm motor retention and a kevlar leader.

I made some real progress tonight, it's starting to come together. I'm basically following the Estes plans. I epoxied all 6 fins on. I took my time I did them one at a time to make sure they went on straight, which was easy, as Leo did an excellent job on getting the curvature to match the body tube. I made sure to work the epoxy into the holes I drilled and I roughed up the back of the fin pads with sandpaper to further help with adhesion. I also tried to keep the amount of epoxy I used low making sure to get a nice even thin coat that wouldn't ooze out.

Man, that is so cool. Looking good!

Use tape to hold the cable covers in place while the glue dries.

I finished it tonight. I used vinyl stickers from Stickershock. Of course after I got all the stickers on I realized I forgot to paint the top of the nose white. Doh! But that's okay. I might spray is with some dull coat to make the decals not so shiny, or a may just leave it alone. Turned out just fine the way it is as far as I'm concerned

Looks Great, Tim! What did the final weight come in at?

Yes, it does look great! What slicer software did you use? Thanks.

Sorry for the delay, school started up and that's a busy time of year for my work.

A whopping 535 grams. As I got further into the assembly it became apparent it was going to be significantly heavier than I expected, so I did switch gears on the engine mount. Luckily I was able to cut out the 24 mm mount without too much trouble and replace it with a 29mm mount. I didn't go crazy with epoxy gluing the fins on, only one coat of paint, no primer. Still came out 535 grams. I know if I had to do it again, the conduits and charge retainers would be balsa and card stock, and based on my experience with the TLP kit, making balsa fins was not that hard. I'd likely just print the nose cone, which really came out awesome, and call it a day.

Ultimaker Cura

Launched it today on a 29mm Econojet F42-4T. Perfect flight and recovery! 4 second delay was just right. Used two 24 inch chutes.

Tim-

Nice series of launch photos...I know you were happy to have a good flight.

What altitude do you estimate you got out of the F? That Pershing design, with such relatively small fins for hobby rockets, always seems like they should just penwheel right off the launch rod. Did you get any ‘tail wag’ on it as it headed up?


Earl